The method is used to operate the drive device or the exhaust gas purification device, which is a component of the drive device. In addition to the exhaust gas purification device, the drive device is equipped with a drive unit, which is provided as a drive unit generating exhaust gas and in this respect generates exhaust gas during its operation.
The drive unit can be provided for example as an internal combustion engine, as a fuel cell or the like. The exhaust gas produced by the drive unit is supplied to the exhaust gas purification device, in particular before the exhaust gas is released into the external environment of the drive device.
The pollutants are removed from the exhaust gas at least partially by means of an exhaust gas purification device. For this purpose, the exhaust gas purification device is provided with at least one catalytic converter through which the exhaust gas of the drive unit can flow in the form of the exhaust stream. The exhaust gas stream device is also associated with two lambda sensors, in particular the first lambda sensor and the second lambda sensor. The first lambda sensor is arranged upstream of the catalytic converter and the second lambda sensor is arranged downstream of the catalytic converter in the exhaust gas stream. At the same time, the two lambda sensor protrude for example into the exhaust gas stream.
The oxygen gas content in the exhaust gas is determined by means of both lambda sensors in the respective positions upstream or downstream of the catalytic converter. The oxygen content can be also determined by means of the first lambda sensors upstream of the catalytic converter, or fluidically between the internal combustion engine and the catalytic converter, and the oxygen content is determined by means of the second lambda sensor downstream of the catalytic converter, in particular fluidically between the catalytic converter and a tailpipe. The first lambda sensor provides a first lambda signal and the second lambda sensor provides a second lambda signal, wherein a first lambda value can be determined from the first lambda signal and a second lambda value can be determined from the latter.
The catalytic converter is provided with an oxygen storage device, or it itself operates as such. This means that in the presence of lean exhaust gas—which is to say in the case when the oxygen excess during the combustions with lambda is greater than one—oxygen passes from the exhaust gas into the oxygen storage device and it is intermediately stored therein. On the other hand, when rich exhaust gas is present—which is the result of combustion with a fuel excess having a lower lambda value than one—the oxygen stored in the oxygen storage device will be removed. In this manner, it is ensured that the stoichiometric ratio, which is necessary for gas purification, can be provided with a lambda value that is equal at least approximately to 1, at least for a certain period of time. The greater the oxygen storage capacity of the catalytic converter, the more oxygen can be temporarily stored in it or in the oxygen storage device, so that a longer period of time can be bridged over with a combustion air ratio that deviates from lambda equals 1.
In particular, the first lambda sensor, which is arranged upstream of the catalytic converter, often has only a low accuracy. For example, if the first lambda signal provided by it deviates by a certain value, the so-called offset error from the actual combustion air ratio in the exhaust gas will occur at the location of the first lambda sensor. As a result of this error, it can happen that the internal combustion engine will be adjusted to a mixture of the composition of the fuel-air mixture that is supplied to the internal combustion engine which deviates from what is required to achieve a good or better conversion performance of the catalytic converter.
Accordingly, the object is to compensate for the error of the first lambda sensor or for the offset error as quickly as possible. This can be done for example by means of a controller which regulates the second lambda signal provided by the second lambda sensor to create a target value. However, this regulation can only be carried out with a very low control speed because control fluctuations occur when a higher speed is used, which in turn leads to a deteriorated conversion performance of the catalytic converter. The regulation of the second lambda signal in order to create a lambda target value is referred to as trimming control. Within the scope of the trimming control, a correction value is determined for the first lambda signal, which is intended to compensate for the offset error. The correction value can in this respect also be referred to as an offset value.
For example, the combustion air ratio is now to be set to a lambda target value, in particular by means of the first lambda signal provided by the first lambda sensor. The lambda target value is preferably determined from a preset lambda value. Conversely, it is of course also possible to determine the first lambda value with the aid of the offset value from the first lambda signal. In other words, the first lambda value is in this case determined from the first lambda signal, so that the first lambda signal is first corrected by means of the offset value. The control variable applied for this control is thus determined from the preset lambda value, from the first lambda value, or from the first lambda value and the offset value. The present lambda value preferably corresponds to lambda equals one.
From prior art is known for example the document DE 10 2012 019 907 A1. It relates to a method for operating an internal combustion engine with an exhaust gas purification device, wherein the gas purification device is provided with a catalytic converter through which an exhaust gas stream of the internal combustion engine can flow, as well as with a lambda sensor arranged upstream of the catalytic converter in the exhaust gas flow, and with a second lambda sensor arranged downstream of the catalytic converter in the exhaust gas flow.